Anaerobic co-digestion of waste activated oily-biological sludge with sugarcane bagasse using thermo-chemical pre-treatment under thermophilic condition

Abstract

Oily-biological sludge generated in large quantities from oil refineries' wastewater treatment plants poses a significant environmental hazard. This study investigates the potential of converting this sludge into energy through anaerobic digestion, producing biogas. Given the sludge's suboptimal carbon to nitrogen (C/N) ratio, sugarcane bagasse, which has a higher C/N ratio, was co-digested with the sludge to enhance biogas yield. Batch co-digestion tests were conducted under thermophilic conditions (55 °C, pH 6.5–8.0, and 60 RPM mixing) to determine the best C/N ratio for biogas production. The raw materials underwent mechanical and thermal-chemical pretreatment using Sodium Hydroxide to improve digestion efficiency. Sugarcane bagasse was treated with 1% Sodium Hydroxide at a 1:10 solid-liquid ratio, 100 °C, and 150 RPM for one hour, while the oily-biological sludge was treated with 1 g/L Sodium Hydroxide under the same conditions. Results from a 33 day batch experiment indicated a positive correlation between increased C/N ratio and biogas yield. The highest biogas and methane yields were at a C/N ratio of 30.0, achieving 202.71 mL of biogas and 76.25 mL CH4 per gram of volatile solids removed. These yields were 72.57 and 77.26% higher, respectively, compared to those at a C/N ratio of 20.0.